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Thanks for the comments and the photos. However, I still don't understand why a control system that rotates the rudder relative to the stock rather than the stock relative to the boat won't work. I realize that with a conventional rudder that pivots about a bolt through the stock there's a significant sideways load unless the rudder is close to vertical. But surely the point is that when trimming a foiled rudder it's rotating relative to the transom anyway but only by a small amount about the vertical position. Why does it matter whether this small rotation is achieved by rotating the rudder relative to the stock or the stock relative to the boat? I was thinking of developing a trimming system based on a Topper type rudder stock and tiller. The idea would be to introduce some 'play' between the stock and tiller with the rudder in the down position and then move the tiller relative to the stock using a control system like the one Dare has developed. As the tiller moves relative to the stock the rudder would be rotated and the foils trimmed. Please could someone explain the error in my logic before I make a mistake?

Thanks again,

Marcus

Having now seen some T foiling boats in action at the Inlands and read the discussion threads relating to T foils I'm interested in building one for my boat. However, before commiting to building one I want to make sure I understand what the foil is doing and I also have some questions relating to aspects that I'm not clear on yet.
 
As I understand it the foil is normally trimmed to produce a positive lifting force that assists in raising the back of the boat out of the water thereby reducing wetted area and the associated drag. The resultant lifting force acts upwards from the foils so the further back from the boat they are located then the more effective they will be because they will provide more leverage (I assume this is why boats like the 14 put the rudder and foils on a gantry that extents behind the boat). However, because the lifting force acts aft of the rudder support points not only will these points be sheared upwards, the lower support will be pulled aft and the upper one pushed forward with these pulling and pushing forces increasing as the foils are located further back. In addition, the supports are loaded in this manner by the drag force acting on the rudder and foils. At present there appear to be two approaches to trimming the foils: in the DCB/Foolish system the rudder pivots about the fixed upper support point and the lower support is pulled forward by a purchase system to overcome the aftwards pulling effect that the lift and drag forces from the foils and rudder create. In the Paradigm type system the setup is reversed, the rudder pivots about a lower fixed point and the upper support is pulled aftwards by a purchase system to overcome the forward push.
 
Now for my first question: if the rudder were located in a conventional stock that attached to fixed rather than pivoting pintles would it be possible to control foil trim simply by rotating the rudder relative to the stock in the usual way? If the vertical line of action of the lifting force were directed approximately through the pivot point then the purchase required to trim the foils would surely be reduced and the control system could possibly be contained entirely within the rudder/stock /tiller assembly itself. Infact, if the line of action of the lifting force were ahead of the pivot point then it would tend to rotate the bottom of the rudder forward as required when generating positive lift although the drag force would still oppose this.
 
My second question concerns the positioning of the foils on the rudder itself: is there a concensus on how far down the blade they should be located to maximize their effect? At the bottom of the rudder the water probably only flows over the foils at the speed of the boat but in the wake region near the top of the rudder the flow speed relative to the foils may be faster and therefore more lift generated. There are probably other aspects to consider in positioning the foils such as the practicalities of tacking and gybing and launch and recovery.
 
Sorry for the rather long and technical posting but I'd like to hear what others think or have discovered.
 
Thanks,
 
Marcus 

Thanks Patrick and everyone else, we also enjoyed the latter two races on the Saturday and were especially pleased with our performance in the pub quiz! It was good talking to people about their experiences with foiling rudders on Sunday morning as well so although we didn't go racing the time wasn't completely wasted. 
Marcus, N3503

We're also planning to be there so two more for food on the Saturday night please.
Thanks, Marcus, N3503

Unfortunately I broke my mast while racing at Loch Lomond last weekend, not the nice carbon one I have on my twelve but the older alloy one I have on my canoe. Since canoes and twelves use similar mast sections I was wondering whether anyone had either an alloy or possibly even a carbon mast that they no longer require and would be prepared to part with? Thanks, Marcus   

Alistair, in my boat, N3503, I have a buoyancy arrangement that isn't quite double bottomed, there's a conventional low stern tank that runs athwartships from gunwale to gunwale but extends 900mm forward of the stern. The front tank extends back to the shroud base at centreboard box capping height. This leaves footwells for both the helm and crew formed by the hull skin itself. We've found this arrangement much more comfortable than a double bottomed boat, the boat has 'sit in it' feel rather than a 'sit on it' feel. In addition, the boat can be sailed to windward immediately after a capsize; any water in the footwells drains in seconds through a pair of conventional bailers that are actually a size smaller than those usually found in a conventional boat. I basically copied the arrangement from one of Rob Peebles' boats, 3396. I always thought Rob had some good ideas in this area; he actually wrote a newsletter article explaining these about 15 years ago now. It's a pity really that the class went down the easy route of full double bottoms perhaps we should of adopted the ideas he was promoting to retain the comfort of a single bottomed boat. There are photos of both my boat and 3396 under the appropriate entries on the boat database. If you were to go down this route you could probably get away with either 4mm ply or even 3mm sheet sheathed with some lightweight glass cloth because neither the helm nor crew would be standing on the tanks when moving about the boat.

Does anyone have an RWO R4520 or similar mast ram sitting around unused? I'm interested in acquiring one! Thanks, Marcus.

I recently had a sail in one of the Winder built Merlins with a one string system for adjusting the rake of the rig and was very impressed by its ease of adjustment. My question is would such a system be suitable for a Twelve? I can see that such a system would make rake adjustment going upwind more staightforward and it would be easy to get the rig upright for going downwind on a run. However, as I understand things the conventional practice of letting the shrouds off going downwind in a Twelve achieves more than just getting the rig more upright, it also allows the mast to straighten thereby producing a fuller sail and enables the boom to be squared off more because of the loose leeward shroud. With a one string system the rig tension would presumably be maintained as the rig is pulled upright so the latter two benefits would not necessarily be achieved. So, what's most important, getting the rig upright, straight or slack? The reason I'm asking is that I sail at a venue where we beat and run a lot but because I usually have one of the kids crewing I often leave the rig alone going down the run since there's enough to do without having to let off each shroud independently as well. Nevertheless a simple one string system for getting the rig upright might be manageable but would I get any real benefit?      

Crew still available! I guess if we were going to Salcombe I would have had lots of enquiries by now. Pity it's so far away from us!

I still have one boat and two crew!

I'm planning to take my boat to Bass week at the beginning of August. However, I have two people who want to crew for me, my thirteen year old son and my nine year old daughter. If anyone was thinking of taking their twelve or similar boat along and requires a crew then give me a ring on 0141 584 9694 (evenings). Both are competent and have the full vocabulary of technical language!

The the limiting factor is NOT necessarily the distance between the base of the mast and the turning block at the shroud plate. On my boat, N3503, there's no fordeck, just a low bow tank so I've been able to run the system forward to the stem via a turning block at the mast foot. Since the mast foot to stem dimension is bigger it gives me a bit more travel for the system. I copied the system off an old International 14. It might just be possible to see it in the photos of the boat on the database. 
The other really important factor with pulley systems is to ensure that the rope stretches as little as possible. The implication of this is obvious: don't invest in expensive ball bearing blocks and then string them together with cheap stretchy rope, particularly in the high tension parts of the system!    

Dad, why are all those other boats in front of us?

Dad, what are you doing?

Some photos of Zoe, my nine year old daughter, and I sailing the boat on Loch Lomond, September 2009 (courtesy John McGruer, LLSC). 
Dad, smile for the camera!